Modern electronic devices are becoming so small and their electrical terminals are so delicate and closely spaced that it is difficult and expensive to make electrical connections by soldering or other established techniques. U.S. Pat. No. 4,113,981 (Fujita et al.) uses an adhesive layer to make individual electrical connections between two banks of electrodes. The adhesive layer includes spherical electrically conductive particles of substantially the same thickness as the adhesive, thus providing a conductive path through each particle that bridges facing pairs of electrodes. The particles are randomly distributed throughout the adhesive layer, but the Fujita patent indicates that if the particles comprise less than 30% by volume of the layer, they will be sufficiently spaced so that the intervening adhesive will insulate against short circuiting between laterally adjacent electrodes. Carbon powder, SiC powder and metal powder are said to be useful.
When the electrode banks cannot be superimposed, Fujita would use a tape as shown in FIGS. 1 and 2 including "terminals 5a of a film conductor 5" (col. 2, lines 56-57), which terminals 5a appear to be continuous metallic strips.
U.S. Pat. No. 3,359,145 (Salyer et al.) makes electrically conductive adhesive connections by filling a "hardenable organic adhesive" (col. 2, line 48) with particles having ferromagnetic cores and electrically conductive surfaces. Two electrodes are joined by the adhesive while it is in a mobile state and, while the adhesive is hardening, a magnetic field is applied in the normal direction, thus aligning the particles to form conductive bridges between the electrodes. Preferred particles have an iron core coated with an electrically conductive metal such as silver which is more resistant to oxidation. Preferably the particles are elongated, and their lengths equal or slightly exceed the bond thickness. Any manufacturer of electrical equipment who wished to use Salyer's method to make electrical equipment would need to procure apparatus for creating a suitable magnetic field and to develop the capability of using that apparatus to position that field correctly. Also, special precautions would be necessary if the electrodes to be connected were part of a device which could be damaged by a strong magnetic field.
Salyer does not teach how to electrically interconnect electrodes which cannot be superimposed.
U.S. Pat. No. 3,132,204 (Giellerup) shows a pressure-sensitive adhesive tape wherein "one or more stripes 13 of electrically conductive material are laid over the upper face of the pressure-sensitive adhesive layer, as shown in FIG. 1 of the drawings, and the tape is then passed between a pair of pressure rollers which compact and flatten the stripes of metal foil (particles?) and the adhesive" (col. 2, lines 2-8). "The compacting of the adhesive and the stripes of metal powder increases the conductivity of the electrically conductive metal powders, without coating the metal particles with the adhesive material" (col. 2, lines 35-38). Although we find no teaching in Geillerup of how to use his tape to make electrical connections, it can be assumed that he intended to use it to make individual electrical connections between two banks of electrodes which cannot be superimposed, with the pressure-sensitive adhesive serving to hold each end of the tape to the substrate of one bank.